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Matt Aufderheide

Doom 3 light glow effect

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If you've played Doom3, i'm sure you have noticed that many lights in the game have a sort of volumetric glow around them.. I have tried to figure out exactly how this is done, but really cant find much info. i suspect it may be some kind of depth rendering trick, but i dont know.. does anyone have any idea what the procedure for this is?

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I don't know if the following technics is used in Doom III to realize the glow effect, but one way would be to render the scene to a texture, blur this texture and blend it additivly back on the original scene. This technics can be used for the whole scene or only for parts, but then you have to use multipass rendering.

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Doom 3 does some cheap little sprite-based glow method which is basically the same thing that's been employed since the Unreal 1 days. You do some sort of occlusion test to see if the light is visible, then overlay the glow sprite over it. You can fade the alpha value in and out as the lights state of occlusion changes to give it a more elegant look. There are some more interesting ways of getting a glow effect these days with all the performance and shaders we have. You can look into glow buffers, where you basically render all the glowy objects in the scene to a low res render target, then blur it and stretch it over the final scene and additive-blend it on there. For higher end hardware (R300/NV40 cards) you can use high dynamic range rendering to give an even more authentic and somewhat automated glow that is a byproduct of lighting calculations. But like I said earlier, Doom 3 just uses sprite overlays to accomplish the "glow" effect. It's simple, cheap, and old school, but it works if that's what you're looking for.

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Quote:
Original post by Matt Aufderheide
If you've played Doom3, i'm sure you have noticed that many lights in the game have a sort of volumetric glow around them.. I have tried to figure out exactly how this is done, but really cant find much info. i suspect it may be some kind of depth rendering trick, but i dont know.. does anyone have any idea what the procedure for this is?


I have played doom3, but now i cann't remember anything about light glowing.
Maybe you can post a screenshot to make it clearer for us to understand...

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Sure i know how to do glow and bloom etc.. but i really dont think the glow effect in Doom3 is done with a sprite.. if you look closely, it doesnt move or rotate like a sprite will.. instead it appears to be volumetric.. you can see similar efects in the AMPII engine demo.. unless i'm totally wrong :)
here's apic of what im talking about in Doom3:
http://matt.brightwatch.com/glow.jpg

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D3 uses a variety of techniques. Usually, I think, it's a kind of sprite, but it's drawn to match the shape of the light emitting polygon. IIRC, if you switch to a wireframe view the glow appears to be formed by creating a polygonal fan around the emitting polygon, drawn so that the points appear approximately equidistant from its edge with respect to the camera. You can see the polygons by the vertex colouring around the glow in this shot.

That said, this one looks like it's done by blurring. I hadn't seen that done in D3 before. Not sure if it's a promo shot or what. I guess it could depend on the hardware.

And the flashlight is volumetric, along with the occasional flashing beacon.

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None of the lighting effects are done with blurring in Doom3. It's all overlayed sprites and light volumes. The same goes for any form of real bloom. It's just not in the engine.

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Guest Anonymous Poster
I'd like to recommend http://www.frustum.org demos - Cold Cathode and Shadow Volume. Neon lamps there are done in way simliar to Doom 3. Sources for both demos are available.

P.S.: Sorry for my English. :)

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In a similar vein, the Unreal engine has had an interesting volumetric light effect since Unreal 2. Remember those lighthouse-type red beacons you had to follow during one level? The effect was much more rounded than Doom 3's, although I suspect they take a similar approach. I haven't been able to work out exactly what that approach is though.

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